Magnetic work holder



Sept. 2, 1952 w BQWER 2,609,430

MAGNETIC WORK HOLDER Filed Jan. 26.1 195o HEM/0 I /o a /nven Patented Sept. 2, 1952 UNITED STATES PATENT OFFICE MAGNETIC WORK HOLDER William L.- Bower, Sheiield, England, assigner to James Neill & Company (Sheffield) Limited, Sheflield, England, a British company Application January 26, 1950, Serial No. 140,642 In Great Britain January 21, 1949 'work holder of this type, i. e., the magnets, co-nductor bars of magnetic material and the necessary insulation between them, are all separately formed and then assembled into a pack and secured together by through bolts. In manufacturing such articles in numbers it is, of course, important toachieve maximum eillciency and regularity of performance as between individual worl: holdersl of a batchconstructed to a common specification for a Agiven duty, and this involves both precisioninthe manufacture of the elements themselves and precision in their assembly into the magnet pack, and from the point of view of magneticLV eliiciency the bestand fullest use possible of the magnetic elements. y

VKThe present invention is designed to achieve these objects and moreover to provide a method of manufacture which will be more rapid and economical than' that hitherto adopted. The conception underlying the invention. is that vby suitabie methods the non-magnetic material necessarily employed for isolation purposes can also be used for the consolidation ofvr the parts into a solid unitary structure. I' p The preferred method of accomplishing this according to the ,invention is by first forming the 'conductor bars or Ymagnets in the form of a grid and then positioning the magnets or conductor bars of magnetic material as the case may be and casting the non-magnetic material-usually vwhite metal-into this grid-like pack so that the whole isA mechanically consolidated with the magnet and .conductor bar elements united but magnetically isolated from one another. v

This method of manufacture results in' advanboth in the expedition of assembly and in both mechanical and magnetic eiiiciency, since apart from the solidity and regularity of the iinished packs the conductor bars can be cast in tapered form and the necessity for rolling special taper section material, as would otherwise be necessary if this taper formv is adopted, is avoided; and since thereare no bolts passing through the structure there is no diminution of the magnetic Amaterial and a smaller and more A'compact `structure for a` given duty) results. l The invention, therefore, in its broadest aspect consists of a magnetic work holder of the type defined wherein the magnets and conductor bars of magnetic material forming the magnet assembly or pack are united mechanically and isolated magnetically by non-magnetic material cast into the spaces between them.

In its preferred form, a chuck according to the invention consists of a casting of magnetic material comprising a series of conductor bars formed as a grid, permanent magnets inserted in the grid lspaces between the conductor bars, said magnets being isolated from the conductor bars by cast-in non-magneticr material.

The invention also comprises the method of manufacture of magnetic work holders of the type dened according to which the conductor bars of magnetic material and magnets are positioned in predetermined spaced relation and united into a solid structure by casting non-magnetic material into the spaces between them.

The accompanying drawings illustrate by way of example a preferred form of magnetic Work holder according to the invention.

In the drawings:

Figure l is a plan view partly in section of the improved magnetic work holder,

Figure 2 is a Section on the line II-II of Figure 1,

Figure 3 is a section on the line I'III-III of Figure l,

Figure 4 is a part section of Figure 1 on the line IV-IV.

The holder comprises a hollow rectangular casing built up from a mild steel base plate I, a rectangular frame of aluminium bronze 2 which conn stitutes the walls of the casing and a top plate 3 whose upper face constitutes the work holding surface. The top plate is formed with seven parallel slots extending across almost the full width of the interior of the casing and within each of these slots there is located a pole piece 4 which is of the same thickness as the body of the top plate and like it is made of high permeability magnetic material. The pole piece is slightly narrower and shorter than the slot in which it is located, the gap between the pole piece and the body of the top plate being completely filled by castingvin white metal 5, so that the pole pieces 4 are integrally united with the body of the top plate 3 but are magnetically isolated from it.

The magnet assembly is slidably disposed within the casing and its construction constitutes the present invention. In the particular construction illustrated the assembly or pack comprises top plate but the bar at one end is shorter, leav-` ing at one corner of the grid an approximately rectangular recess 9 which accommodates the con- .trol gear described below.` rhe spaces between the conductor bars l receive ve long and one short permanently magnetised bars lll which are of the same depth as the conductor bars, sothat their polar faces engage the base and top plates respectively. The permanent magnets are slightly narrower and shorter than the spaces in the grid within which they are accommodated, and after they have Ybeen positioned the gaps between thernand the magnetic material conductor barsof the grid are filled by casting in White metal H, so that the magnets are mechanically united with the grid to form a solid block or pack, but are magnetically isolated from the grid. In order that the white `metal may securely hold the magnets in position in the grid, the longitudinal members 8 ofthe grid have the inner side of their lower edges beveled oil as at 8a and the bars 1 are slightly tapered in thickness in the upward direction to the level, erv adjacent the level, of the top of the longitudinal member. This tapering of the bars is advantageous in that by the dispersion of the magnetic flux over the major portionof thelength it permits` the use of a material such as silicon iron and enhances results where high permeability materials are employed'.V The permanent magnets are formed with projecting flanges lea which extend along the whole length of their upper edges and for a short distance from each end of their lower edges.

The operating gear is accommodated in the cut away corner of theA magnet assembly. It ccmprises a crank handle l2 secured on the reduced outer end of a horizontal shaft i3 which passes rotatably through a thickened part of the side Wall 2 of the casing. The shaft is retained in position by a vertical bolt i4 which engages an annular groove l5 in the shaft. rlhe reduced cuter end of the shaft is surrounded by a cup washer i6 which prevents the escape of oil from the casing. Integrally formed on the inner end of the shaft is an eccentric pin il which engages rotatably in a hole in the outer endof a connecting link I8 extending longitudinally of the casing. The inner end of this link is received betweenthe short longitudinal member Sa of the grid which bounds the space for the short magnet and a lug 'lb projecting from the adjacent magnetic material conductor bar, the link being connected to these parts by a pivot pin i?! preferably offset from the centre line of the eccentric pin Il. Rotation of the shaft through 180 produces the required longitudinal displacement of the magnet'assembly, the movement being limited by the engagement of a projecting portion iSd of the connecting link with the base plate I of the casing.

When the operating handle is in the on position, the upper faces of the permanent magnets I, which are arranged with like poles uppermost, lie immediately beneath and in contact with the under surfaces of the portions y3d of the top plate 3 left standing between the slots in that plate,

these portions of the top plate being of the same width (measured longitudinally of the casing) as the upper surfaces of the magnets. The upper faces of the magnetic material conductor bars 1 lie immediately beneath and in contact with the inserted pole pieces d of the top plate, those pole pieces being of the samewidth (measured longitudinally of the casing) as the upper surfaces of the intermediate bars 1; the two end bars are off lesser Width. Thus, when the magnet assembly is in the position described and a work piece of magnetic material is resting on the upper face cf the top plate 3, a magnetic circuit is established from -the upper pole of a magnet l0,

vthrough the body of the top plate 3, the work piece, an inserted pole piece 4 of the top plate, a magnetic material conductor bar 1 of the grid and the base plate 3, back to the lower pole of the magnet. When the operating handle is moved to the on position, the magnet assembly is shifted towardshthe other end of the casing through such a distance that-the gaps between the permanent inagnets i() and the magneticvmaterial conductor bars 'i are bridged on one side of the magnets by the body of the top plate 3 and on the other side of the Vmagnets by the inserted pole pieces 4 of the top plate. A magnetic circuit from the upper to the lower pole or" each magnet ish-thus completed through the top plate 3, magnetic material conductor bars 'l and base plate l, substantially the whole of the magnetic flux being -shunted out ofthe work piece, which can accordingly be removed` readily.

The invention is` not of course limited to the precise construction described above, many modincations being possible so long as the fundamental conception of first arranging a grid structure of the magnets and magnetic material vconductor bars and then consolidating and uniting the parts yinto a solid structure by casting in the non-magnetic material is preserved, For ex,- ample, in the construction shown and described the conductor barsare formed vas anrin'tegral casting. It would, of course, be possible, but with less advantage t form this grid structure from separate parts welded or riveted together. It would also be possible, again with less advantage, to form the grid of the magnet material and then position separate magnetic material conductor bars as inserts and unite by casting in the nonmagnetic material.

'It will be understood that vfor large sizes the grid structure may be 'triade `up f two or more grid units connected together prior t'o the casting in bf the neri-magnetic material to eifect the unity and consolidation of the magnets and the conductor bars.

By means ofthe invention thevne'c'essity fo'r securing bolts Vin the ymagnet 'assembly is entirely eliminated the nen-magnetic vn'ate'rial being utilised to perform Athe two fold function 'of eiecting the necessary isolati'n of the parts and their amalgamation 'into a solid structure.

I claim:

AA magnetic workyholder, comprising a top plate of magnetic material formed with a plurality 'of transversely disposed `parallel slots therein, an equal plurality of pole pieces of magnetic inaterial, each disposed in one of said slots in said topplate, Yeachvof said pole pieces having a thickness equal to that of said top plate and a length and a width less than those of the corresponding slot, thereby forming an annular gap about eachvpole piec`e ,nonmagnetic material filling the annular gaps between said pole pieces and said top plate, a base plate of magnetic material disposed in spaced parallel relation to said top plate, a frame of non-magnetic material eX- tending between said top plate and said base plate and secured to each of them, said top plate, frame and base plate together constituting a closed hollow casing, a grid of magnetic material slidably disposed within said casing, said grid including a plurality of transversely disposed parallel tapering conductor bars of magnetic material extending the full length of the interior of the casing, said conductor bars tapering in an upward direction so that the bases of said bars are wider than their upper ends, and a pair of longitudinal members connecting together the ends of said conductor bars and of lesser depth so as to be spaced apart from said top plate, said conductor bars and longitudinal members together dening a plurality of transverse recesses extending through the thickness of said grid, a plurality of permanent magnets, each disposed in one of said recesses and having their polar faces engaged with the inner surfaces of said top and base plates respectively, each of said magnets having a length and width less than REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,507,777 Karasick Sept. 9, '1924 1,970,922 Simmons Aug. 21, 1934 2,179,625 Groden Nov. 14, 1939 2,234,968 Hayes Mar. 18, 1941 2,271,904 Watelet e Feb. 3, 1942 2,376,150 Karasick May 15, 1945 2,404,072 Karasick July 16, 1946 

